Yanmar 2QM15- Out of Ideas

[WestcoastCrown]

I'm hoping the collective knowledge of the forum can point me in the right direction.

Background:
Engine is 1978 2QM15 with apporx 1400 hours. P/O was very good but decided to sell due to advancing age. Did $3K worth of work 40 engines hours ago. Head, injectors etc.

Boat saw little use for past 5 years, but was serviced & run regularly.

Current:
Boat has been motoring along fine and then rpm drops and comes back, repeats repeats. Engine will not die.

Replaced;

Filters and all fuel lines. Same problem after 3 straight hours of motoring.
Install new Racor primary today, bleed, and it runs like a clock.

Go out for one hour, throttle up, throttle down try to recreate problem, doesnt happen. Yippee!

200 meters from slip doing 2.5 knots, engine does it again!! sputter, regain sputter, regain, never dies.

New bowl on filter looks clear, no water at all. Everything tight.

Any thoughts??
Thank you in advance.
Kevin

[Opie91]

Could be some type of fuel supply issue.

Not a complete list but check for:

Air leak on vac side, fuel pump, bad fuel pickup in tank, or my personal favorite something floating around in the tank and getting sucked into the pickup. Once you shut the boat down it falls off the fuel pickup and everything is fine until you suck it up again.

[Rocketman]

This sounds like a fuel related problem, check and recheck everything fuel related, that means all joints where there is a nut on a fuel line, and then check the fuel tank pickup. Somewhere you are starving the fuel system of fuel or air is getting in. You might also check the air intake, some of the yanmars have a crappy foam airfilter that will desenigrate with age, throw it a way you don't need it. If you can not find anything wrong with any of these things, try taking a clean 5 gal fuel can and pulling fuel directly from it instead of the onboard tank. Might be something blocking the fuel pickup. Good luck.

[Charlie]

Try putting a short clear piece of hose in the fuel system so that you can see if there are air bubbles in the fuel. Seems odd since you changed the fuel line but that is where the symptoms point IMHO

[boden36]

Have you checked that your tank has a clear air vent?
Regards,
Richard.

[WestcoastCrown]

Thank you for the ideas. I will check the vent line to see if thats it, and then try running from a 5 gallon diesel can. That will narrow down the problem area very quickly. Now I just have to pray that I won't have to pull out the fuel tank.....
Cheers,
Kevin

[sammyo]

Interesting, had (hopefully past tense) on a 2QM20H. Emptying the fuel and changing filters seemed to help but for other reasons I'm dealing with a head gasket and have not been running much. These engines have a pretty simple governor but there is a spring involved, I wonder if that's something that can be checked? I'll keep and eye on this thread.

[Cheechako]

Good Idea on the air vent. I had little bees plug up my vents once. Took hours to clear it out. Generally, If you are starved for fuel the engine will speed up a little; so it doesnt sound like you arent getting enoug fuel.. You can disconnect the vent tube at the tank and blow on it to see if it's clear. Could also be pinched somewhere. If it is venting, I would be tempted to buy an electric fuel pump at NAPA and install it in line between tank and filter. If that cures the problem you'll know where to look. IF it doesnt, it's great for filling/bleeding after fuel filter changes. My Brother in Law used to build those Crown 34's. Sturdy built boats! A lot of variation boat to boat though.

[WestcoastCrown]

Quick update: After reading all of the posts and speaking to a certified diesel mechanic, he suggested I crack the bleed screw before the next start to see if fuel is present there, or if the fuel system had lost its prime.
So after the boat sat for three days, I tried it. Undid the bleed screw and had to pump the lift pump lever many times to see fuel. So I have a leak somewhere, which was suggested in many responses. I have ordered all new crush washers and gaskets for every connection around the secondary filter and lift pump & will replace this weekend. - At which point it will run flawlessy for years to come! ( have to keep the dream.)

The mechanic did not feel it was the governor as the problem is intermittent. Apparently governors tend to either "work or fail".

I still have not checked the air vent, but will do so on the weekend.

Cheechako: Yes, they are a very well built boat. I did not know a lot about them prior to buying it, but am very pleased with it. Going from a Columbia 26 to this boat is a world of difference, please tell your BIL "thanks".

More to come.

[Cheechako]

There may have been a couple of builders of that boat, and If I remember right, the mold came from a renouned designer and wasnt called the Crown 34. Unfortunately, I cant remember the pedigree. But a 34 footer with a good solid skeg and strong, but not over heavy, layup is not that easy to find really. I never sailed one though.

[sailorchic34]

Hum... A air leak that's big enough to effect the engine at speed, yet not shut it down and then go away, and repeat is a interesting air leak. Does the engine start up easy. If so its not much of an air leak. When you open the bleed screw your letting air in and fuel can drain a little back to the tank ,if its lower then the bleed port. Also maybe a internal leak / bad valve on the fuel pump

So hows your water lift muffler. Any odd chance that your getting a big spurt of water about the time the engine speeds back up. Check the discharge elbow, just for fun... it might be partly clogged from mineral buildup.. that could do it.

I'd still not totally discount the governor. After a blocked discharge ell, that would be my next thought...maybe a loose bit somewhere effecting it.

[WestcoastCrown]

Quick Update on this little adventure:
Replaced all of the gaskets/washers around the secondary filter and bled it out. Left it for 48 hours and she started up quite quickly. So took it out for a spin & motored along at about 2300 RPM for 20 mins before it started dropping and regaining RPM. Sat at anchor for about 1.5 hrs before heading back, but this time ran at about 1900 RPM and it purred like a kitten! Flawless all the way home.

Have now pulled the exhaust elbow and found it to be not clogged ( and as I have no experience with this cannot say a percentage of blockage) but have wire brushed and sand blasted it internally. It looks brand new inside and is in great shape. So will head back out to the boat to re-install elbow, new exhaust hose and new fuel tank vent hose.

Hopefully these steps will be the solution. If not, I will set up a diesel can to run off to rule out the fuel tank as the problem.

Fingers crossed.

[Cheechako]

It's sounding a little like the tank pickup tube clogged...?

[charliehows]

ive had a few issues with air leaks on my 2qm20 recently - airleak from a fuel filter fitted wrongly, engine started, ran died. loose hose clamp, engine started, ran, died. Your problem doesnt sound like an air leak because once air gets in the system the engine conks, it wont recover. id be looking at a blockage in the fuel tank, setting up a 'day' tank to test it sounds like a pretty good idea to me. how long do you get out of your anodes? my front one wears away a lot quicker than the back one.

[Nikos Baillie]

I agree it sounds like a blockage. Never hurts to replace all fuel lines. An air leak wouldn't result in what your describing.